The invention relates to a ski alarm system and provides an alarm unit for a ski which allows the ski to be detected when buried in snow. Such a unit has use in detecting the whereabouts of a skier who may have been buried in an accident and also in finding lost skis. A preferred feature of the invention is the additional use of the unit in detecting attempted theft of skis.
According to the invention there is provided an alarm unit for ski comprising a sounder for emitting an audible alarm signal. A battery powered circuit connected to energize the sounder. A movement responsive unit is connected to the circuit, the circuit including a timer and being arranged to activate the sounder when the movement responsive unit has given no output representative of movement for a predetermined time.
The alarm unit may, instead of being designed as an accessory to be fixed to a ski, be incorporated in the ski binding.
There have been proposed hitherto arrangements in which a ski alarm is activated on removal of the ski from the boot or on automatic actuation of the ski brake. Unlike the present invention, such systems are of no use in detecting buried skiers who have retained their skis.
Preferably the circuit has at least two modes to which it may be set, namely a ski mode in which, as described above, lack of movement is caused to energize the sounder, and a theft mode in which the converse is true, and the sounder is energized on detection of movement by the movement-responsive unit.
Preferably the circuit has additionally a test mode in which the alarm functions may be tested and a standby mode in which the circuit is clear to be set to one of the other modes. Mode setting may be accomplished by mechanical or magnetic reed switches associated with the alarm unit. Preferably, however, a remote control unit is provided. The remote control unit may effect control by audio signals, perhaps of ultrasonic frequencies or by radio control. Preferably, however, the remote control unit is an infra-red transmitter which issues coded infra-red signals to a receiver unit incorporated in the alarm unit.
Preferably the movement responsive unit comprises a housing with walls, internal electrodes on different walls of the housing and a number of discrete electrically conductive members in the housing which are free to move and which rest in contact with each other and with the electrodes to form a conductive bridge between the electrodes, movement of the members being effective to change the resistance presented by the members between the electrodes. The members are preferably metal balls. The housing may be oil-filled.
The sounder is preferably a piezo-electric unit. Extensive experiments have established that in typical operating conditions there is an optimum frequency range which, for a given power output, offers the best sound detection and position location characteristics. This frequency range is between 2000 and 4000 Hz.